The spectral characteristics of chlorine-containing water clusters in the presence of ozone and oxygen

The infrared absorption and Raman spectra were calculated by the molecular dynamics method for water clusters with chlorine ions in a medium of water and ozone or oxygen molecules. The intensity of IR absorption spectra of clusters with absorbed oxygen increased and that of clusters with absorbed ozone decreased as the number of chlorine ions grew. Excitation strengthening caused by an increase in the number of Cl⁻ ions weakened the intensity of Raman spectra when either oxygen or ozone was absorbed; for ozone, this weakening was more noticeable.     

Molecular dynamics calculation of spectral characteristics of water clusters in the presence of ozone molecules and chlorine ions

Simultaneous interaction of the (H₂O)₅₀ cluster with O₃ molecules and Cl⁻ ions was studied by the molecular dynamics method. Six O₃ molecules located near the cluster were absorbed by the aqueous aggregate, and Cl⁻ ions in turn left the zone of the interaction with the cluster. Some of Cl⁻ ions penetrated inside the formed (O₃)₆(H₂O)₅₀ cluster and come into collision with O₃ molecules that split the ozone molecule into atoms. When Cl⁻ ions were removed sufficiently far away from the cluster, the water cluster with absorbed O₃ molecules and O atoms was observed for 15.6 ps. The interaction of water molecules with Cl⁻ ions gives rise to an increase in the integral intensity of absorption and emission IR spectra, and also to an essential decrease in the analogous characteristics of the Raman spectrum in the frequency range of 0 ≤ ω ≤ 1000 cm⁻¹. The presence of Cl⁻ ions did not affect essentially the location of the main band in the IR spectra, but considerably changed the shape of the bands in the Raman spectrum.     

Calculation of spectral characteristics of water clusters upon interaction with oxygen molecules and bromine ions

Interactions of (Br⁻) _i (H₂O)_50−i clusters (0 ≤ i ≤ 6) with molecular oxygen is studied by the molecular dynamics method using flexible molecule model. Values of real and imaginary parts of permittivity decrease in the 0 ≤ ω ≤ 3500 cm⁻¹ frequency range with increasing number of bromine ions in a cluster. The ability of cluster to absorb IR radiation decreases, whereas the reflectance and Raman light scattering remains nearly unchanged. An increase in the content of Br⁻ ions in the cluster lowers the power of emitted IR radiation and decreases the amount of active electrons participating in the interaction with IR radiation. However, when the concentration of Brions becomes substantially higher (at i = 5 and 6), the values of emitted power and the number of active electrons are restored to the values that are typical for water cluster in the absence of Br⁻ ions. At i ≥ 3, repelling Br⁻ ions acquire kinetic energy, which is sufficient to remove molecular oxygen from the system.     

Computer simulation of oxygen and nitrate ion absorption by water clusters

Using the molecular dynamics method, the joint absorption of oxygen and nitrate ions by water clusters is studied in terms of the polarizable model of flexible molecules. Significant fluctuations are observed in the number of hydrogen bonds in the clusters during the addition of NO₃⁻ ions to water-oxygen aggregates. Dielectric permittivity noticeably changes upon the addition of O₂ molecules to water clusters and nitrate ions to oxygen-containing water clusters. After the absorption of oxygen molecules and nitrate ions, water clusters markedly lose the ability to IR absorption. The Raman spectrum of a medium formed from disperse aqueous system, oxygen, and nitrate ions displays a greater number of bands than the spectrum of a system of pure water clusters.     

Spectral characteristics of water clusters upon interaction with oxygen molecules and chlorine ions

The interactions of a 6O₂ + (H₂O)₅₀ system with two, four, or six Cl⁻ ions are studied by the molecular dynamics method. The integral intensity of IR and Raman spectra decreases with an increase in the number of Cl⁻ ions surrounding the system. The values of real and imaginary parts of dielectric permittivity increase with the rise in the frequency reaching maxima in the 850 ≤ ω ≤ 950 cm⁻¹. As a result of interactions between ions and the formed (O₂)₆ (H₂O)₅₀ cluster, the pattern of the reflection spectrum of IR radiation becomes smoother. The interaction between 6O₂ + (H₂O)₅₀ system and Cl⁻ ions leads to the substantial increase in the power of emitted radiation. With time, Cl⁻ ions gradually leave the interaction zone with the system. Maximum residence time of the last ion near the system boundary does not exceed 3 ps. Cl⁻ ions located closer to O₂ molecules do not penetrate into the depth of an (O₂)₆ (H₂O)₅₀ cluster.     

IR and Raman spectroscopic study of the photopolymerization of Langmuir-Blodgett films of acetylenic acids

The UV induced photopolymerization of Langmuir-Blodgett films of lead salt of 2-docosynoic acid (CH₃(CH₂)₁₈C=CCOOH) is studied using IR and Raman spectroscopy. It is found that the films are a highly ordered system with trans-configuration of alkyl chains and a bridged complex generated between the carboxyl group and the lead ion. Based on a change in the absorption band intensity in the IR spectra corresponding to the triple bond vibration, the degree of polymerization depending on the irradiation time is determined. In the Raman spectra, a peak at ∼1635 cm⁻¹ appears during polymerization, which corresponds to the C=C double bond. The formation of conjugated double bonds in these systems is observed for the first time. During polymerization, methylene chains of molecules retain trans-configuration; the structural ordering of molecules in the film is observed.     

Concerning the problem of temperature changes in the intensity of continuous absorption in the spectra of complexes with symmetric H-bond

The effect of temperature on the spectra of anharmonic vibrations of complexes with symmetric H-bonds was simulated and considered using H₃O₂ ⁻ and H₅O₂ ⁺ ions as an example. The intensity of continuous absorption observed in the IR spectra of such types of complexes is virtually independent of temperature. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1447–1449, August, 1997.     

Structure of BaTiO<Subscript>3</Subscript> phases is studied by comparing neutron diffraction and Raman spectroscopy data

Considering the structural unit of the rhombohedral BaTiO₃ phase in the form of Ti(-O...Ti)₆ which was constructed by neutron diffraction data, we revealed an atomic group in the form of a pyramidal complex anion TiO₃²⁻. Inspection of the Raman spectra of this phase showed symmetry group C _s for this complex anion. From the similarity of the Raman spectra of all ferroelectric BaTiO₃ phases, we inferred that the orthorhombic phase and tetragonal phase are also built of TiO₃²⁻ complex anions. In the paraelectric cubic phase, TiO₃²⁻ complex anions decompose to oxygen ions O²⁻ and Ti²⁺(O⁻)₂ molecules, which are randomly oriented over 12 possible positions. Average Ti-O distances derived from neutron diffraction data were used to calculate Ti-O⁻ and Ti=O bond lengths in TiO₃²⁻ complex anions of the ferroelectric BaTiO₃ phases. Two types of Ti-O...Ti bridges were found to exist; they belong to weak and strong intermolecular bonds, which are similar to weak and strong hydrogen bonds (H-bonds) in ferroelectrics. Weak bonds exist in all of the three ferroelectric phases; strong bonds are only in the orthorhombic phase and the tetragonal phase. As a result of a low potential barrier height in strong bonds, an oxygen atom persistently hops from one potential well to an adjacent one, which is responsible for bands appearing below 100 cm⁻¹ in the Raman spectra of the tetragonal phase and orthorhombic phase. The data obtained on the structure of the ferroelectric BaTiO₃ phases were used to interpret their spontaneous polarization, repolarization, and permittivity.     

Conductivity of semiconducting tin dioxide in dry air caused by oxygen chemical transformations and chemisorption

The conductivity of semiconducting tin dioxide (SnO₂) in pure nitrogen and dry air was studied over the temperature range ∼20−650°C. Conductivity was shown to be caused by chemical transformations of oxygen molecules on catalytically active oxide surfaces. It unambiguously corresponded to the formation of O⁻ and O²⁻ chemisorbed ions. The experimental data were used to construct the temperature dependences of the chemisorption of O⁻ and O²⁻. The formation of O⁻ ions was maximum at ≈200°C, and the formation of O²⁻ ions did not reach a maximum at 650°C and increased beyond this limit. The number of electrons entrapped by chemisorbed oxygen ions and the concentrations of oxygen ions at all formation stages were estimated.     

An IR spectroscopic study of acid centers on the surface of Al,Zr silica gels

Acid centers of Al, Zr silica gels with approximately equal aluminum ion contents (∼2.4% Al₂O₃) and various concentrations of Zr ions were studied by IR spectroscopy using the deuteroacetonitrile molecule as a probe. The surface of such samples was found to contain Lewis acid centers of two types, coordination unsaturated (I) silicon and (II) zirconium ions. An increase in the content of zirconium ions was accompanied by a decrease in the intensity of the 2328 cm⁻¹ band in the IR spectra. This band was characteristic of interaction of CD₃CN with Lewis acid centers of type I. The suggestion was made that this was caused by a decrease in the accessibility of coordination unsaturated silicon ions to CD₃CN molecules.     

Infrared spectroscopic study of the structure of the tetrabutyl S-dithiopyrophosphate complex of silver

The structure of the complex Ag·TBDTPP (tetrabutyl S-dithiopyrophosphate) formed in HNO₃ medium was studied by IR and NMR methods. The complex is involved in the isomerization of TBDTPP in the presence of Ag⁺ and NO ₃ ⁻ ions. In the IR spectra, we observe the disappearance of P−O−P band and the occurrence of new absorption bands associated with P−S−P and P=O bonds. The silver ion is coordinated to the thiophosphoryl group of the isomer molecule. The influence of HNO₃ concentration on complex formation is discussed.     

Study of temperature effect on uni-univalent and uni-bivalent ion exchange reaction

Ion exchange equilibrium constant (K) for Cl⁻/Br⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 30 to 45°C. For both uni-univalent and uni-bivalent exchange systems, the value of K increases with rise in temperature i.e., from 1.16 at 30°C to 2.95 at 45°C for Cl⁻/Br⁻ system and 19.5 at 30°C to 30.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. The article is published in the original.     

Regularities of photostimulated conversions in nanometer aluminum layers

The gravimetric and optical spectroscopic methods reveals that light irradiation with λ = 300–750 nm and intensity I = 6.9 × 10¹⁴–1.1 × 10¹⁶ quanta cm⁻² s⁻¹ for τ = 1–160 min in atmospheric conditions significantly changes the absorption and reflection spectra and mass of aluminum films (d = 2–200 nm). The kinetic curves of the degree of conversion versus aluminum film thickness are satisfactorily described in the inverse logarithmic and parabolic terms. The contact potential difference is measured for Al and Al₂O₃ films along with the photo-EMF of Al-Al₂O₃ systems. The suggested model includes the stages of generation and redistribution of nonequilibrium charge carriers in the contact field of Al-Al₂O₃ systems, oxygen adsorption, Al³⁺ diffusion, and Al₂O₃ formation.     

Study on ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion-exchange resin Duolite A-113

The study on thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻, and uni-divalent Cl⁻/SO₄²⁻, Cl⁻/C₂O₄²⁻ reaction systems was carried out using ion-exchange resin Duolite A-113. The equilibrium constant K was calculated by taking into account the activity coefficient of ions both in solution as well as in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems were observed to increase with rise in temperature, indicating the endothermic exchange reactions having enthalpy values of 17.21, 36.60, 19.50, 18.43 kJ/mol respectively.     

Raman spectroscopic investigation of the antimalarial agent mefloquine

The antimalarial agent mefloquine was investigated using Fourier transform near-infrared (FT NIR) Raman and FT IR spectroscopy. The IR and Raman spectra were calculated with the help of density functional theory (DFT) and a very good agreement with the experimental spectra was achieved. These DFT calculations were applied to unambiguously assign the prominent features in the experimental vibrational spectra. The calculation of the potential energy distribution (PED) and the atomic displacements provide further valuable insight into the molecular vibrations. The most prominent NIR Raman bands at 1,363 cm⁻¹ and 1,434 cm⁻¹ are due to C=C stretching (in the quinoline part of mefloquine) and CH₂ wagging vibrations, while the most intense IR peaks at 1,314 cm⁻¹; 1,147 cm⁻¹; and 1,109 cm⁻¹ mainly consist of ring breathings and δCH (quinoline); C–F stretchings; and asymmetric ring breathings, C–O stretching as well as CH₂ twisting/rockings located at the piperidine moiety. Since the active agent (mefloquine) is usually present in very low concentrations within the biological samples, UV resonance Raman spectra of physiological solutions of mefloquine were recorded. By employing the detailed non-resonant mode assignment it was also possible to unambiguously identify the resonantly enhanced modes at 1,619 cm⁻¹, 1,603 cm⁻¹ and 1,586 cm⁻¹ in the UV Raman spectra as high symmetric C=C stretching vibrations in the quinoline part of mefloquine. These spectroscopic results are important for the interpretation of upcoming in vitro and in vivo mefloquine target interaction experiments.     

In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

Modeling the infrared and raman spectra of silicon dioxide clusters absorbing water

The effect of absorbed water on the dielectric properties of silicon dioxide nanoparticles is studied by the molecular dynamic method. It is demonstrated using the model of flexible molecules that increasing the number of water molecules in the (SiO₂)₅₀ cluster to 40 results in an enhancement of absorption of infrared radiation over the frequency range 0 cm⁻¹ ≤ ω ≤ 1000 cm⁻¹. It is ascertained that the absorption of water molecules by the (SiO₂)₅₀ cluster considerably alters the shape of Raman spectra of light, smoothing all the peaks after the first one, and that water molecules are concentrated near the cluster surface formed by SiO₂ structural units.     

Some applications of positron annihilation lifetime spectroscopy to complex formation and ion association studies

The rate constants for the reactions of positronium with halogen molecules and with halide ions in methanol (I₂, Br₂, Cl⁻, Br⁻) and in dimethylsulphoxide (I₂, Cl⁻) have been measured. The variations of the ortho-positronium lifetime in mixtures of these solutes have been used for quantitative determination of the formation constants of the corresponding polyhalides. These were found to be 2.9 and 5.4 M⁻¹, respectively, for I₂Cl⁻ and I₂Br⁻ in methanol and 2.0 M⁻¹ for I₂Cl⁻ in dimethylsulphoxide. Experiments on acidified AgClO₄ solutions confirmed the formation, at molar concentrations, of the Ag₂ ClO ₄ ⁺ species, very probably a triplet ion association.     

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C <Subscript>1</Subscript>E<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C <Subscript>1</Subscript> (<Emphasis Type="Italic">n</Emphasis>=1−4)

The hypothesis that the degree of hydration of poly(oxyethylene) (POE) in aqueous solution depends on the mole ratio of water molecules to ether oxygen atoms in the molecule has been verified by studying the isotropic Raman spectra in the O−H stretching region for four short-chain POEs (C ₁E _n C ₁ withn=1−4). Excellent coincidence of the O−H stretching Raman band for all four POEs studied in the range of mole ratio H₂O/O _ether from 25 to 0.6 was observed, thus confirming the assumption stated above. A conclusion that all ether oxygen atoms in the POE molecule participate in hydrogen bonding with water molecules has been made.     

Spectral characteristics of aqueous dispersions enriched in oxygen

The IR absorption and reflection spectra of aqueous dispersions consisting of (H₂O)_n, O₂(H₂O)_n, and (O₂)₂(H₂O)_n clusters (10 ≤ n ≤ 50) were calculated by the method of molecular dynamics using a flexible model of molecules. The frequency distribution of the power scattered by the cluster systems was obtained in the range 0 ≤ ω ≤ 3000 cm^?1. The capture of one oxygen molecule by the clusters is accompanied by a decrease in the absorption of the low-frequency IR radiation and by a peak of the absorption intensity in the vicinity of ω 2704 cm^?1. This is also accompanied by a decrease in the reflection coefficient throughout the frequency range and a decrease in the emission power at ω < 1030 and ω > 1700 cm^?1. Addition of two oxygen molecules to the clusters decreases the capability of the dispersions for the absorption, reflection, and scattering of IR radiation.